Nowadays, modern motor vehicles have in many cases a plurality of driver assistance systems that can assist the driver and intervene, for example, in critical situations, or in the best case help to avoid these critical situations. Such driver assistance systems comprise anti-lock brake systems (ABS), electronic stability adjusters (ESC, ESP, traction control systems), transmission controllers for automatic transmissions, shift aids, shift assistance and/or drag torque controllers (SMR, DTC), a ride level controller (ECAS) and/or an offroad mode, and can also include other systems.
Some driver assistance systems such as ABS or ESC, ESP and traction control systems have speed sensors on each wheel in order to detect automatically the speed at which each wheel is rotating. If differences are detected here, this can indicate a slippery roadway with a low coefficient of friction. These systems are usually based on the principle of measuring the rotational speed of the vehicle wheels. The speed sensors may be of purely mechanical design, but they usually now operate with inductive sensors or Hall sensors in a contact-free fashion. The speed sensors can be mounted on each wheel, such as is customary, for example, in ABS systems. However, these systems have the disadvantage that they cannot detect a low coefficient of friction and therefore a potentially dangerous situation until differences in wheel speed are detected, that is when the vehicle is already skidding.
Other driver assistance systems such as SMR or automatic transmissions generally do not have any information whatsoever about the state of the roadway, with the result that, for example when shifting into a relatively low gear speed, critical driving states can be caused by the engine braking torque.